The present invention relates to a thermal bend actuator. More particularly, the present invention relates to a thermal bend actuator and to a micro-electromechanical device.
Recently, for example, in PCT Application No. PCT/AU98/00550 the present applicant has proposed an inkjet printing device which utilizes micro-electromechanical (MEMS) processing techniques in the construction of a thermal bend actuator type device for the ejection of fluid from a nozzle chamber.
The aforementioned application discloses an actuator which is substantially exposed to an external atmosphere, often adjacent a print media surface. This is likely to lead to substantial operational problems in that the exposed actuator could be damaged by foreign objects or paper dust etc. leading to a malfunction.
According to a first aspect of the invention, there is provided a thermal bend actuator which includes
a wafer substrate;
an elongate actuator arm that is fixed to the substrate at a fixed end, the elongate actuator arm including a heater layer of a conductive material and a dielectric, resiliently flexible layer, the heater layer defining a heater circuit which is connected to an electrical potential;
a working member that is fixed to an opposite free end of the actuator arm; and
control logic circuitry that is positioned on the substrate, between, and generally aligned with, the heater layer and the substrate, the control logic circuitry being interconnected between a data input means and the heater circuit and including register circuitry connected to the data input means to generate an enabling signal and firing circuitry connected between the register circuitry and the heater circuit to close the heater circuit on receipt of the enabling signal so that said electrical potential generates a current in the heater circuit, resistively to heat the heater layer, at least the heater layer being of a material having a coefficient of thermal expansion which is such that the heater layer can expand on heating and contract on cooling to do work, the heater layer being positioned so that the elongate actuator arm experiences differential thermal expansion and contraction and thus reciprocally displaces the working member.
The control logic circuitry may be configured so that traces defining the circuitry extend substantially at right angles with respect to a longitudinal axis of the actuator arm.
The heater layer may define corrugations in regions that are aligned with the control circuitry, the corrugations extending substantially at right angles to the longitudinal axis of the actuator arm.
The heater layer may define a transverse discontinuity such that a portion of the heater layer defines the heating circuit and is connected to the control logic circuitry and a remaining portion of the heater layer defines a structural supporting layer for the actuator arm.
The actuator may include a bend compensator layer that is positioned so that the dielectric layer is interposed between the heater layer and the bend compensator layer, the bend compensator layer being substantially identical to the heater layer.
According to a second aspect of the invention, there is provided a micro-electromechanical device that comprises
a substrate; and
a plurality of thermal bend actuators that are positioned on the substrate, each thermal bend actuator comprising
an elongate actuator arm that is fixed to the substrate at a fixed end, the elongate actuator arm including a heater layer of a conductive material and a dielectric, resiliently flexible layer, the heater layer defining a heater circuit which is connected to an electrical potential;
a working member that is fixed to an opposite free end of the actuator arm; and
control logic circuitry that is positioned on the substrate between, and generally aligned with, the heater layer and the substrate, the control logic circuitry being interconnected between a data input means and each heater circuit and including register circuitry connected to the data input means to generate an enabling signal and firing circuitry connected between the register circuitry and the heater circuit to close the heater circuit on receipt of the enabling signal so that said electrical potential generates a current in the heater circuit, to resistively heat the heater layer, at least the heater layer being of a material having a coefficient of thermal expansion which is such that the heater layer can expand on heating and contract on cooling to do work, the heater layer being positioned so that the elongate actuator arm experiences differential thermal expansion and contraction and thus reciprocally displaces the working member.
According to a third aspect of the invention, there is provided an inkjet printhead formed on a silicon wafer and including a plurality of nozzle devices, each nozzle device comprising a nozzle chamber and an aperture through which ink from the nozzle chamber is ejected, an actuator for applying pressure to ink within the nozzle chamber to cause ejection of an ink drop through the aperture, and drive circuitry for controlling the actuator, wherein the drive circuitry and the actuator share area of said silicon wafer.
Preferably the actuator and the drive circuitry overlap.
Preferably the actuator overlies the drive circuitry.
Preferably the actuator is external to the nozzle chamber.
Preferably the actuator is a thermal bend actuator.
Preferably the actuator is attached to a paddle which resides within the nozzle chamber.